Apparently there was a patchset regarding snapshot functionality to ext4, which was even mentioned on phoronix: http://www.phoronix.com/scan.php?pag...item&px=OTU0Mg

The patches: https://github.com/amir73il/ext4-snapshots/

I wonder what happened to them. They were proposed to be integrated into 3.0, but disappeared without trace.